If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

I glued the faces on and finished the rough sanding for the two cabinets. I'll need to repaint where the material that was removed from the sides/faces (~1/8" all around plus that portion of the box that extended beyond the faces). That's a lot of sanding and my hands and arms haven't been this tired since I was a teenager.

I also need to stain the cabinets. I am trying to decide if I should do the paint up, or stain first. Probably stain. Opinions?

We are currently having strong Santa Ana winds, and any painting will have to wait.

Meanwhile, I think that I will mount the speakers and see if there is anything to be gained by going with open baffles. (Could be an epiphany!) This might be the better way to go with the Heils.

I can either just use a capacitor to block the bass, or set my speakers as "small" and let the Yamaha roll them off below 200 Hz and run them full range. Could be interesting.

OK..., got some RTA screen shots showing the open vs closed back with the 2251Js in ~1/2 cu ft cabinets. The only filtering being used is a 33.6 mfd cap inline with the positive terminal and the speaker is set to "large."

The microphone was placed inline between the two speakers at a distance of 2 meters on a tripod sitting on the couch cushion (legs in). "Close" micing was not performed because this defeats the purpose of the open back. No eq of any type is being used. Of course this does include the effects of the room.

The intent is to run these from ~250 to ~2,500 Hz.

Note that with the closed back, the frequency response "falls" as the frequency is reduced such that between 250 and 2,500 Hz there is a span of about 16 dB (i.e., -83 to -67 dB).

But with the open back, the frequency response remains fairly flat dropping substantially below the crossover point, which is essentially what we want here. The span is reduced to about 9 dB (i.e., -74 to -65). The overall volume is also louder.

It is interesting that even though the closed back sounds like it has more bass, the open back must by responding with things/reflections in the room causing more deep bass. I am simply switching between the two speakers and recording the results without any provisions to equalize their volume. What you see is what the mic hears.

I have found that while no back is better than having a full back..., having some back can produce a flatter bass response than no back. Therefore, I'll cut both backs down to two strips to go along the bottom to hold the terminal cup, and the top to match, leaving about 31.5 sq in in open. This is also roughly the area of the cone so we'll see how that goes.

Meanwhile, I pulled the back off the other one and have each sitting on an L200/300 cabinet. These are wired with 35 mfd in series with the positive lead to the "B" speaker output though my speaker switcher that allows for volume matching. I actually have these turned down by ~8 dB according to the panel markings.

I'm loving it! If you look at the RTA plots you will see that the 2251Js have a nice little "bump" that fills in the gap left by the crossover between the 2235 and 2420. Then you get a near perfect natural rolloff to the 2405 with no electrial filter necessary! Vocals and cymbols become so much clearer, or there where they weren't before. I should have done this years ago.

Actually, I'm betting that the 2251J could easily replace the 2420/horn all together, go much lower, and would be smoother doing it. May just need to turn off the horns and give this a try.

Review of the Heil spectrum revels that the "hole" in the midrange associated with the ESS AMT series is due to the fact that the Heils have a natural roll-off well above their crossover point. I find that you really don't want to take the Heils below ~4KHz.

You can't make a driver do what it can't do without compromising the sound, so rather than try to make the Heil reach down to ~2,500 Hz, we will run parallel band pass filters into the 10".

One filter is between ~210 and 4,500 Hz. This protects the woofer at the lower end, brings the ~4K peak down to that a 1K, and meets the Heil on the top end (47 mfd/~0.4mH). Graphic shows a sealed cabinet. I've found that if I port the cabinet, I can increase the low end to make the 210 crossover point.

The other filter is between ~1 and 3.5 kHZ. This will smooth out the dip which looks to be pretty much "1st order." (~6 mfd/~1 mH). Mills resistors will be used to balance the two circuits.

It's time consuming winding coils, substituting lots of cap values, and analyzing and comparing results, but we'll get there.

I've been working out the crossover and decided that based on the characteristics of the drivers, the parts on hand, available part values, and costs, I would set the crossover points at 160 Hz from the 2241H to the 2251J, and 3,340 Hz to the Heil AMT. I was trying to work this out to avoid L-pads, but the ear is too sensitive to small changes and readily available discreet components provide too course of changes.

I've not seen an issue running the heils below 4k- in fact, one of the best attributes about them is their upper midrange/lower treble capabilities- the folded diaphragm has as much surface area as an 8" (but one with minimal xmax capability). With care they can readily crossover well below traditional domes, in the 1500hz range, or even lower if you can give them the right acoustic environment (a waveguide bumps the bottom end up, I've run them happily at 1300hz and up)

Don't use acoustic rolloff alone, particularly on a compression driver. Excursion increases for most of these drivers faster or as fast as the inherent rolloff of the driver/horn combo, as frequency decreases.

With this many drivers to work with, you might consider a transient-perfect design- duelund described it, possibly others, where a 12dB rolloff on either end of the passband for a mid, with clean 12dB lowpass below and highpass above, and the phase inverted on the mid. You get a nice flat phase response if you can align drivers well.

With respect to open vs. closed back bass, the ultimate enclosure for most mids is a damped line. Basically a TL, but without intending to grab output from the backwave, just damp it. This damps the drivers fs peak and makes crossover work much easier (and more effective at power limiting at Fb vs. a conventional box, unless you include an impedance trap).

You're welcome to drop by, I still do have the multichannel amp and XO you're welcome to borrow as you're working through this. I took two days off thurs 2/15 and fri 2/16, and may have an open house to get rid of gear, if I can get it all tested, photographed, etc., in the next couple days. I want to cash out on a lot of my old efforts and reclaim my garage for the wife's new ride.

You're welcome to drop by, I still do have the multichannel amp and XO you're welcome to borrow as you're working through this. I took two days off thurs 2/15 and fri 2/16, and may have an open house to get rid of gear, if I can get it all tested, photographed, etc., in the next couple days. I want to cash out on a lot of my old efforts and reclaim my garage for the wife's new ride.

Thanks, looking forward to it.

At this point I've gone all passive. This allows me to use the speakers all together with the L200/300 or in two separate sets. The 18"/10"/Heil is actually about 3 dB lower than the L200/300. I can balance this through my system when used simultaneously, but if I do, the 10" becomes too "present." I have L-pads on the way (currently discreet values), that will allow me to adjust the volume to the 10" and the Heil independently to better dial in the system.

You are welcome to come by and hear this any time. Hey you need a break!

I'm still working on the crossovers (very close) and have yet to address the lack of any padding in the 18" cabinet, and to reduce their tuning frequency a bit. Hear you can hear them when compared to the L200/300. I've been trying to get that dark cloud off Joni's voice for years. This seems to do it.

Today I cut out the faces for the crossovers. These will be stained in black and the white lettering will stand out. Note that the lettering was printed inverse to show through. The pots will get new clear backings with their functions in white.